Giuliani also said he thinks the GOP business mogul will get more than 50 percent in the New York primary, which is the threshold necessary for triggering a winner-take-all allocation of the statewide delegates.

But the former New York mayor clarified to The New York Times that he's not formally endorsing Trump; he's just voting for him in the state's primary. He said Trump is "not the man you see on television ... he's a gentleman, he's a good father."

Still, Giuliani didn't shy away from criticizing some of Trump's decisions -- including his decision to go after Heidi Cruz, the wife of Texas Sen. Ted Cruz. "I didn't like that," Giuliani said, qualifying it by adding: "He's a first-time candidate -- you're going to have some of these mistakes."

New York's primary will be a major indicator of whether Trump is able to get the 1,237 delegates necessary to secure the Republican nomination outright. Ninety-five delegates are at stake in New York.

"It's a question of how much he gets over 50 percent. If he wins 70 to 80 delegates, Donald has a good shot of securing the 1,237 delegates to secure the nomination before the convention," Giuliani said.

In the same interview, Giuliani blasted Cruz for his criticism of "New York values" on the campaign trail--a comment that's getting him in trouble now that he's campaigning in the Empire State.

"I know he was attacking liberal Democratic values ... I know," he said. "I fought to change those policies in areas like welfare reform and policing, as did Mike Bloomberg. ... There was a better way to say it."

Trump, too, has piled on in regard to those comments. His campaign released an Instagram video attacking Cruz over them on Thursday: